1. Technical Field
The present disclosure relates to a camera system for use during surgery and, more particularly, a camera system for use during minimally-invasive surgery.
2. Related Art
Currently, video camera system design for surgical applications has to meet a number of challenging requirements imposed by operating conditions that are not encountered in other professional video applications. These include considerations in areas such as patient safety related to leakage current and electromagnetic interference and compatibility, ease of use by surgeons, a compact size that minimizes clutters around the operating tables, consistent image quality while maintaining interoperability of equipment with different optics and camera control electronics in different operating rooms, elimination of fogging in wet environments, and equipment reliability under harsh sterilization conditions. Other requirements may also need to be considered. These requirements translate into engineering challenges in the design and manufacturing of the mechanical housing, optical components, cable interconnect components, and electronics circuitry.
The most unique attribute of an endoscopy camera designed for minimally invasive surgery, driven by the ease of use requirements, is the two-part design where a compact camera head containing an imaging sensor (e.g., charge coupled device or CCD) is separated from the camera control unit (CCU) containing the video processing electronics. The compact head must fit inside the palm of a surgeon, in as small and as non-intrusive a package as possible. The raw, unprocessed video signal must be transmitted through a thin flexible cable, typically four meters long, to the CCU. Present camera systems mostly operate with analog video signal transmission to the CCU, which introduces unit-to-unit variability of image quality. Temporal drifts in the gain, offset and phase properties of the analog electronics in the camera head and the CCU, cable impedance, transmission delay and losses, all contribute to the variability in the system performance and must be compensated. In a typical hospital, the CCU's are fixed in operating rooms, while the camera head and endoscopes are pooled as they must be sent after each procedure to cleaning and sterilization. The random assignment of camera heads to CCU's presents a challenge to the manufacturers' ability to meet the most important requirement by surgeons, namely, consistently high image quality from procedures to procedures. In many instances, one particular combination of a camera head and a CCU may produce high quality image, while other combinations may be less than satisfactory.
Inconsistent image quality due to mismatch of camera heads and CCU's is one of the most common service problems. This creates a design and manufacturing challenge not encountered in other professional video cameras where the imaging sensors are always packaged, matched to, and calibrated together with the video processing electronics as one single unit. In present endoscopy camera design, which contains many analog electronic components all contributing to a distribution of performance characteristics and stacked-up tolerances, an elaborate video signal alignment procedure must be carried out for both the camera head and the CCU in order to compensate for the unit-to-unit variations. Adding to this complexity, an analog camera head has to be aligned using a calibrated CCU, while a CCU must be aligned using a calibrated camera head. The calibrated camera head and the calibrated CCU are carefully selected to be the ideal or “golden” reference, as this term is known to those of skill in the art, camera head or CCU.
Even if this circular and inter-dependent video alignment procedure is successful, residual variability, drifts, and instability over an extended period of time will inevitably lead to mis-alignment between the camera head and CCU. Finally, camera head video alignment and calibration with the camera control unit is performed manually on the manufacturing floor, thereby wasting valuable time. A system is needed such that automatic calibration and alignment can occur once the camera is connected to the camera control unit.
With the introduction of HDTV cameras for endoscopy applications, the above-described problems are compounded by improved image quality requirements, namely, higher resolution, better color accuracy, lower noise, and as much as six times increase in video bandwidth. The higher bandwidth requirements make the transmission of analog video and timing signals, over a four meter cable, much more challenging. Minor variations in cable lengths that can be compensated with analog phase-lock loops in standard definition television become several times more challenging to correct. As bandwidth is increased, noise and other circuit stability problems are compounded. The electrical power dissipation also scales proportionally higher with increased signal bandwidth, thereby leading to increased heat dissipation. In a compact camera head, the heat generated will further increase the operating temperature of the electronics circuit, resulting in yet higher thermally induced noise and drifts.
To overcome the above problems, and in order to ensure the highest image quality commensurate with the expected benefits of HDTV camera, it is desirable to digitize the video signal inside the camera head, so only digital signals, rather than analog signals, need to be transmitted over a cable to the remote CCU. This approach also has the benefit that the video image quality will not be degraded due to noise pickup along the cable, and the CCU electronics will have no analog circuit that is prone to drifts and instability. If the video signal is 100% digital, no manufacturing calibration or video alignment is needed for the CCU during the manufacturing process, thereby saving time and cost. Several technical hurdles must be overcome in order to send digital data to the CCU.
First, the heat generated by the additional analog-to-digital conversion circuitry within a small confined volume must be dissipated. Second, a high quality, high resolution digital HDTV imaging sensor requires as much as fifty bits of bi-directional data transmission between the camera head and CCU. If these fifty bits of data are sent by a traditional cable where one line is dedicated to one bit, the cable diameter will become too large and inflexible for good user ergonomics. The wire count and cable diameter must be not be bigger or less flexible than the present camera cable diameter, which is about 6 mm, in order to preserve the ease of use by surgeons. Third, in order to be in compliance with international standards for medical devices on electromagnetic interference and electromagnetic compatibility (EMI/EMC), the emission of electromagnetic radiation due to transmission of high bandwidth digital data along a cable must be contained.
Accommodating video camera electronic components that generate heat energy at a relatively high rate, compared to some standard video cameras, requires that the housing be composed of a material with relatively high thermal conductivity, such as aluminum or an aluminum alloy. If a high thermal conductivity metallic alloy is used for the camera housing, the exterior metallic surface must be electrically isolated. The need to be electrically isolated contradicts the requirement that the interior electronics must be surrounded by an electrically grounded Faraday cage, so as to prevent internally generated electromagnetic interference (EMI) from leaking out of the camera housing and affecting safe operations of other medical electronics used in surgery and patient support. At the same time electromagnetic compatibility (EMC) must be ensured, such that normal camera performance is immune from external electromagnetic interference to a level consistent with international standards for medical devices, such as IEC60601-1-2 for EMI/EMC safety. Furthermore, all the surfaces that may come in contact with the patient must be designed to minimize leakage currents and be insulated to withstand dielectric breakdown to a level required by internationally recognized electrical safety standards, such as the IEC60601 or UL2601 Standards for Electrical Safety. These conflicting requirements therefore require a new approach to the design of the camera housing.
The present video camera systems contain image processors or camera control units that are equipped to process the analog signals from the camera head. As stated above, this analog processing creates unwanted system variables. In addition, as also stated above, alignment and calibration of the camera head currently takes place on the manufacturing floor, rather than automatically upon plug-in of the camera head and the camera control unit. Automatic alignment and calibration of the camera head requires a camera control unit that has the ability to process a number of mathematical algorithms in a particular sequence in real time. Furthermore, as technology evolves, a camera control unit is needed that is easily modifiable to support different types of camera heads.
Therefore, there remains a need for a camera system that can accommodate a camera having a higher definition than standard definition, substantially reduces analog variability in the camera head and camera control unit while preserving image quality, and substantially reduces interactions of head electronics, cable impedance, and camera control unit circuits. In addition, a camera control unit that is easily modifiable to support different types of camera heads and has full control of signal processing algorithms so as to process them in real time is also needed. Furthermore, a system is needed whereby alignment and calibration of the camera head is automatic upon plug-in of the camera to the camera control unit.